It's not so much an API change, but rather that Grease Pencil gets created on Scene level instead of Object level by default now. At least the object_grease_scatter one we have handles this correctly, but unfortunately, not all of the ones out there are quite as vigorous.

hi, grease pencil is a widely used tool & important to many peoples workflows.
care should be taken when breaking release addons & popular tools.
as there is no maintainer & I am responsible for it's inclusion in Blender, i'll try to fix &/or try to negotiate fixes with other addons & Blender devs.
this addon should be fixed before 2.73 release as it's wide user base would be very disappointed.

I m kind of understand you but can you make so that Grease Pencils gets created on object as default because many artists use GP to sketch on model and many add-ons rely on that ability for now retopo workflow will get really slow. Please bring those stroke back please.

Hmm... maybe I'll need to implement that switch to set where these get added after all. The impression I get is that for standard (non-old-addon usage), it's better that these are not attached to the object.

It at least gets rid of the immediate problems, but at least from my tests, some other issues were cropping up. I'm not sure if those originated from this fix, or whether they were present in the addon.